Past Imperfect (STO)
From Trekipedia
Stardate Unknown: Stop the Klingon Augments from altering the timeline and rescue Miral Paris.
I've spoken with Starfleet Intelligence. Listen carefully.
You are to use the Guardian portal to follow B'Vat wherever, or whenever, he went. Find him and stop him from altering the past.
Stop the Klingons, save Miral Paris, and restore the timeline.